Fertilized human egg (zygote) during first cleavage stage. Egg has split into two cells.

Human egg seconds after fertilization by a spermatozoon. Male pronucleus not yet formed.

Schematic transverse section through the spermatic cord and its components.

Fertilized human egg (zygote) having reached the blastocyst stage. Zygote contains 20-30 eggs and a fluid-filled blastocele is beginning to form.

Fertilized human egg (zygote) having reached the blastocyst stage. Zygote contains a fluid filled blastocele is preparing for implantation into endometrium of uterus.

Sperm, anatomy and fertilization